As it has already been stated, infinity is not a number... it is merely a concept that tells you something goes on forever. In terms of physics, a plank length is the smallest length that has physical significance. While it may potentially be the smallest unit of how something can be seperated by, it is by no means the smallest number. In math, a number does not have to correspond to nature. The complex numbers are an example of this.

well if infinity is not a number but a concept how do you explain where numbers dont end

like if you draw a circle and start to draw lines from the center accros, and so on until you cant draw them anymore, but you can take a sharper pencil and draw even more lines, there will always be a small gap in between the lines, and this will go on until infinity, because the gap will always remain, so if inifity is not a number why would we even bother using it in mathematics or physics, (i use infinity in calc 3 sometimes, but not in the form as a number tho, just to take certain integrals)